153 



St. Petersburg, June 16, 1859; Imperial Mineralogical Society, 

 St. Petersburg, October 10, 1858, acknowledging the receipt of 

 the publications of the Society ; Verein fiir vaterljindische Natur- 

 kunde in Wiirttemberg, Stuttgart, December 5, 1858 ; Societe de 

 Physique et d'Histoire Naturelle de Geneve, November 20, 

 1858, acknowledging the same, and presenting their own publica- 

 tions ; K. Akademie der Wissenschaften, Wien, January 22, 

 1859 ; Oberhessischer Gesellschaft fiir Natur-und-Heilkunde, Gies- 

 sen, March 30, 1859, presenting their publications; Societe de 

 Geographic, Paris, July 31, 1856, acknowledging the receipt of 

 the Society's publications, and asking for previous numbers ; H. 

 Davis, July 9 and August 8, concerning collection of specimens, 

 &c. 



Messrs. William Sharswood of Philadelphia, and Ar- 

 thur M. Edwards of New York, were elected Corre- 

 sponding Members. 



September 21, 1859. 



T. J. Whittemore, Esq., in the Chair. 



A letter from Mr. William Edwards, of South Natick, 

 Mass., to the President, on the phenomena of vibrating 

 dams, was read, by vote of the Society. 



His observations and experiments had been made during 

 nearly every day for fourteen months, ending with February last, 

 upon the waterfall in that village. The phenomena there ob- 

 served are not confined to the vertical sheet, but may be traced 

 in any rapid stream of water, in the bed of which an obstruction 

 is placed ; the waves or nodes below such an obstruction are 

 identical with those of a vertical sheet obstructed by a dam. The 

 nodes describe the form of the surface, and never move from 

 their place except by an increase or decrease of the amount of 

 water above the obstruction ; by sinking this last the distance be- 

 tween the nodes is increased, by raising it they become more fre- 



